1. Field of the Invention
The present invention relates to a sensorless brushless motor drive apparatus and drive method.
2. Description of Related Art
Japanese Laid-Open (Kokai) Patent Application Publication No. 2009-189176 discloses a synchronous electric motor drive system in which a terminal voltage of a non-energized phase of three phases in a three-phase synchronous electric motor is compared with a reference voltage, and an energization mode is sequentially switched according to a result of the comparison.
In sensorless drive control mentioned above, an induced voltage in the non-energized phase varies due to detection variations of a voltage detection circuit, motor (winding) variations, temperature environments, and so on. This causes a deviation in energization mode switching timing, leading to a decrease in efficiency and step-out.